Patents and patent applications to Charles Swerdlow and/or Mark Kroll, including U.S. Pat. Nos. 9,827,416; 9,821,156; 9,814,876; 9,675,799; 9,636,500; 9,486,624; 9,427,577; 9,272,150; 8,825,158; 8,812,103; 8,700,156 and 8,352,033; U.S. patent application Ser. Nos. 15/810,324; 15/080,343; 15/344,864; 14/224,281 and 14/203,688; PCT Application Nos. PCT/US13/43386; PCT/US13/72957 and PCT/US15/22435; U.S. Provisional Application Ser. Nos. 60/999,041; 61/236,586; 61/689,189; 61/733,713; 61/817,667; 61/834,540; 61/841,107; 62/231,087 and 62/283,104; Foreign Patent Application Ser. Nos. EP2928547A1; EP2859364A1 and EP2854702A1; and their related families are fully incorporated herein by these references. These patents and patent applications are hereinafter referred to as the Swerdlow and Kroll patents.
Additional prior art patents that are also fully incorporated herein by reference include U.S. Pat. Nos. 4,424,551; 5,333,095; 5,896,267; 5,905,627; 5,959,829; 5,973,906; 6,275,369; 6,529,103; 6,765,779; 6,888,715; 7,038,900; 9,492,659 and 9,757,558.
Referring to the '156 and '150 patents, the primary inventive concept was to introduce an RF signal down the lead conductor of the shocking electrode(s) to determine if the electrode has migrated within the patient's body, or if the insulation on the lead conductor has been compromised such as by abrasion, a cut, a break, and the like. The '156 and '150 patents describe that if the shocking electrode migrates too close to the lead conductor or if the insulation on the lead conductor is compromised so that the conductor is exposed to body fluids, during a high voltage shock a large amount of the energy is undesirably dissipated in the wrong area. Consequently, a portion of the high voltage shock is not available to cardiovert the heart, which can lead to death due to ventricular fibrillation.
Inventors Swerdlow and Kroll had conceived of using an RF source and reflective return signal known as the S1,1. In network analysis and in using network analyzers, the S1,1 signal is known as the reflection signal. By analyzing the reflection signal, one can determine whether the high voltage shocking conductor(s) in the lead body indicates compromised performance. Such compromised performance can be from one or more of the following: undesirable electrode migration toward the edge of the lead body, lead abrasion, or a break in lead insulation. Any one of these undesirable events, whether alone or in combination with each other, can reduce the insulation resistance such that shocking energy is lost. Swerdlow and Kroll spent a great deal of time discussing and trying to figure out how to build an EMI filter that would filter out undesirable EMI signals from the shocking lead, for example, the SVC lead pin #10, while at the same time, allowing the interrogation RF source to pass through. Typically, the RF source that does the S1,1 interrogation would be on the order of 125 MHz. The inventors of the present invention pointed out that it would not be possible to design a passive RF filter, such as a feedthrough filter capacitor or a two-terminal MLCC chip capacitor because there are EMI signals involved that are too close in frequency to the S1,1 signal. For example, Tetra radios are being introduced into the marketplace that operate at approximately 150 MHz (to as high as 435 MHz).
Worse yet, MRI compatible active implantable medical devices have become very important. They are called MRI conditionally approved devices. Therefore, an ICD or pacemaker in today's marketplace needs to be MRI conditionally approved for both 1.5 Tesla and 3 Tesla MRI scanners. The RF frequency of 1.5 Tesla scanners is 64 MHz and for 3 Tesla scanners is 128 MHz. Since these RF frequencies are relatively close to the RF interrogation S1,1 signal, it is difficult to build a filter with a notch ranging from 150 MHz to 435 MHz that is not mistaken for a Tesla scanner frequency.
The inventors of the present invention discussed with Swerdlow and Kroll the possibility of using multi-element low pass filters to create a very sharp cutoff frequency. The inventors analyzed a 7-pole Butterworth filter. The inventors also discussed 5 to 8-pole Tchebycheff filters. These types of filters are capable of providing a relatively sharp cutoff frequency, but one that is not sharp enough to attenuate a 128 MHz MRI signal while passing a 125 MHz S1,1 interrogation signal. Furthermore, the high number of elements required for these sharp cutoffs becomes too complicated and too large to fit inside of a modernized ICD. It is difficult enough to fit a single element filter inside an AIMD housing, much less one with 5 to 7 inductor and capacitor elements.
Another problem is that the capacitive elements of the Butterworth and Tchebycheff filter ceramic capacitor-type designs have an aging rate. Even if it were possible to have a sharp enough cutoff to separate a 128 MHz MRI signal from a 125 MHz signals, over time, due to capacitor aging, the Butterworth or Tchebycheff filter characteristic curves would change and their drift might lead then to overlap with the frequency that is intended to be cutoff. In other words, the use of sharp cutoff or notch filters is simply not practical.
Accordingly, the inventors of the present invention have conceived of a novel RF switch that in the normal operating mode is configured to switch the desired conductor pin directly to a filter capacitor, for example a two-terminal MLCC chip capacitor, which is in turn connected to a ferrule ground. In this way, a high degree of EMI filtering is provided to a shocking electrode conductor through the RF switch to the passive EMI filter.